The present invention is directed to a composition and its use in removing scale from a surface. More particularly, the composition includes an aliphatic alpha-hydroxy carboxylic acid, a gum or polymeric thickener and optionally sodium silicate.
The term "scale" generally refers to the accumulated deposits commonly found on water-exposed surfaces. Frequently encountered scale is often made up of carbonates or sulfates of calcium, sodium, potassium, or magnesium. The scale may also contain metal oxides, grease, oil or dirt. The consistency of the scale may vary from brittle and porous to tough and dense. The function of a descalant or descaling agent is to effectively remove these deposits.
Scale can be removed by either mechanically detaching the accumulation of deposits from the surface or by chemically treating the accumulation. A possible method for chemical treatment involves exposing the scale to a strong, inorganic acid solution such as hydrochloric, hydrofluoric or phosphoric acids. However, these acids are toxic and are difficult to handle.
Pierce in U.S. Pat. No. 3,294,689 discloses a synergistic sequestering composition for removing heavy metal ions from an aqueous solution. The composition consisted of a polyhydroxyl amine and one or more water soluble alpha-hydroxy acids. Pierce employs a basic pH and is particularly interested in removing ferrous, cupric, nickelous, aluminium and cadmium cations. He is also interested in removing combinations of cations such as ferrous and ferric; ferric and manganous; ferric, ferrous, manganous and cupric; and ferric, manganeous, cupric, zinc and nickelous.
Lesinski in U.S. Pat. No. 3,308,065 discloses a method for removing scale from metal surfaces. The method involves treating the scale with an aqueous, alkaline, saline solution. The solution employed contained at least one ammonium, amine or hydroxy alkyl amine salt of nitrilotriacetic acid, N-2-hydroxyethylamino diacetic acid, and alkylenepolyamine polycarboxylic acid or mixture thereof.
U.S. Pat. No. 3,699,047 of Petrey discloses a cooling system corrosion inhibitor which comprises a divalent metal ion such zinc, cadmium and mixtures thereof, a chelating agent and a modified lignosulfonate polymeric material. The chelating agent may be an alkylphosphonic acid or salt thereof, a polycarboxylic acid compound such as ethylene-diamine-tetraacetic acid, nitrilotriacetic acid, hydroxyalkyltetraacetic acids and sugar-acid chelates such as sodium heptagluconate such as discussed in Robertson, et al, U.S. Pat. No. 3,256,203.
However, there remains a need for a descalant which may be chiefly used for metal carbonate residues found in hard water which can remove scales effectively and safely without harm to the surface or to the worker.